Automatic combustion control



A g 1940- R. E. BRESSLER ,0

AUTOMATIC COMBUSTIQN CONTROL Filed D80. 10, 1938 (0'41 okrun FEED MOTORP550 REDl/Cl/VG Patented Aug. 20, 1940 AUTOMATIC COMBUSTION CONTROLRobert E. Brcssler, Oregon, m, assignor to Kol- Master Corporation,Oregon, 111., a corporation of Illinois Application December 10, 1938,Serial No. 244,985

' 15 Claims. (Cl. 110-101) This invention relates to improvements inautomatic combustion controls and it consists of the matters hereinafterdescribed and more particularly pointed out in the appended claims. Theimproved control is herein illustrated and will be herein described asused in connection with a stoker for feeding solid fuel' such as coal toa fuel bed and for supplying the air necessary to support combustion.

In stoker fed furnaces, the amount of coal that will be burned by acertain volume of air varies materially with the condition of the fuelbed. Also, the amount of coal that will be fed by the stoker, as whenthe screw or other mechanism is operating at a certain rate will varymaterially with several different factors, one of which is the amount ofcoal in the hopper causing a different quantity to be'fed to the screwor other feed mechanism. The reason therefor is thatthe depth of thecoal over the 'screw or other mechanism varies, and much more coal willbe fed by a full hopper than from one. only half full.

The sizeof coal that is being supplied to the stoker will also make alarge variation in the amount of coal that would be fed and segregationof coal when it is delivered to the bin, even with prepared stoker coal,is such that variation of as much as 30% will be had in the amount offuel being supplied to the burner when the feed is set at' the samesetting when-coarse or fine coal is being supplied.

supplied. Sometimes this excess runs as high as 200'to 300%. so that theefliciency of the stokers is materially reduced as compared to whatcould be had with proper control of both coal and air pplyg The depth ofthe fuel bed on the'bumer or retort determines the pressure of the airin the chamber beneath the fuel bed and this pressure varies with thedepth or density of the fuel. bed. There is a proper fuel bed depth forevery size of stoker and thefuel bed depth, required by the design ofthe burner, does not vary with various burning rates at which the fuelmay be burned.

For proper operation of a stoker, the fuel bed should be maintained atan approximatelyexact depth independent of the rate at which the coal isbeing burned. The pressure in the wind box and chamber beneath theburner or retort will.

7 varied either with increase or decrease of wind box pressure. Wind boxpressure in a stoker as used herein, is the pressure caused by theoperation of the blower using a certain setting of the damper when theair is being delivered through a fuel bed of any particular depth. Inthis respect, the damper may be associated either with the inlet or thedischarge side of the blower.

One of the objects of the present inventionis to provide an automaticcombustion control which maintains a constant fuel bed and supplies 7 afixed volume of air therefor.

Another object of the invention is to provide a control which maintainsa fixed burning rate and which rate may be readily adjusted to provideinnumerable rates to suit conditions without difficulty or danger of toomuch fuel accumulation in the furnace and at the same time reduce flyash to a minimum.

- A further object of the invention is to provide a control of this kindwhich maintains a fixed wind box pressure through control of fuel feedto maintain a fixed fuel bed resistance, by means of the tendency of thewind box pressure to vary. Again, it is an object of the invention topro-.

. limits.

Again, it is another. object of the invention to provide a controlwhich, if the fuel bed is thin, after a stand by period, causes a feedof coal at its maximum feeding rate until the proper. depth of bed isrestored when the coal feed is operated to maintain that depth of fuelbed and to supply coal in accordance with the amount being burned withthe volume of air supplied.

Again, it is a further object of the invention to provide an automaticcombustion control for a stoker wherein no attention need be given thestoker except for the periodic removal of clinkers and supplying coal tothe hopper.

The above mentioned objects of the invention,

as well as others together with the several advantages thereof, willmore fully appear as the specification proceeds.

In the drawing: Fig. 1 is a diagrammatic view of the preferred form ofthe invention in connection with a stoker for controlling the operationthereof.

Fig. 21s a longitudinal vertical sectional view on a somewhat enlargedscale through the retort or burner of the stoker as taken on the line2-2 of Fig. 1.

Fig. 3 is a vertical sectional view on an enlarged scale through acertain pressure switch embodied in the system and which will be laterreferred to.

Referring now in detail to the accompanying drawing, 5 indicates asawhole a conventional stoker including a fuel hopper 6, a burner .orretort 'I and a conduit or. tube 8 leading from the hopper to theburner. In the conduit I is o a screw 9 (see Fig. 2) for moving the fuelalong the conduit into the burner with an underfeed action to pile uptherein over the dead plates ID to provide the fuel bed ll of thedesired depth. The feed screw is rotated step by step by a drivemechanism enclosed in a casing l2 and this mechanism is driven through asuitable speed reducing mechanism l3 from a motor l4. The conduit 8 hasa windbox |5 associated therewith and one end of said windbox is made asan air chamber H3 in which the burner is disposed in a manner wherebyair in said chamber passes into the burner and up through the fuel bedtherein to support combustion. In the discharge duct of the blower,where it connects with the windbox, is a damper |5a operable fromoutside the windbox by a dial I5b. By means of said.

damper, the volume of air entering the windbox may be controlled. Ifdesired, the damper may be placed in the inlet side of the blowerinstead of where described. The other end of the windbox is operativelyconnected to the discharge side of a blower H, the inlet side of whichis hooded as at l8. Preferably, a second and smaller motor I9 isemployed to drive the blower. By the use of the two separate motors asmentioned, it is possible to burn fuel at a lower rate at a smallcurrent cost. One side of the motor I9 is connected to one side of theother motor H by a bridge or line 20.

The improved control includes a plurality of control elements, namely atemperature responsive element suchas a thermostat 2| employed in thearea or space to be heated and a limit control 22, usually placed in thebonnet of a hot air furnace when the stoker is employed with such afurnace. On a hot water furnace, said limit control is clamped to a pipeleading away from the boiler thereof. The control further includes atransformer 23, a relay 24 with a V coil, a second relay 25 with a 24Vcoil, a motor driven time switch 26 with a short interval contacter anda longer interval contacter, a circuit breaker 21 which serves as anoverload protection for the coal feed motor and a pressure actuatedswitch 28.

The transformer 23 serves only, to reduce the voltage in the circuit ofthe room thermostat 2| so that small wire may be used therefor, thussimplifying installation. The relay 24 with the 110V coil controls thecoal feed driving motor I4, the motor being energized when said relay isclosed and decnergized when said relay is open. The' relay 25 with the24V coil is the starting device for the blower motor l9 and also for thecoal feed motor when the relay 24 is closed.

The time switch 26 serves two purposes. A part thereof closes once, sayevery 10 minutes and remains closed for a period of about a half aminute or less. This causes the coal feed motor I4 to operateonce eachthermostat 2| calls for heat independent of all other controls, exceptwhen the circuit breaker 21 is open or the limit control is ofi.. Whenthe circuit breaker is open or when the limit control is off, said motorwill not run. The other part of the interval contacter operates as ahold fire control, closing once each hour for about a minute, causingoperation of the entire stoker for that period except when the limitcontrol is oif or the circuit breaker is open. 1

The pressure switch 28, as shown in Fig. 3, is in the nature of a casing29 containing a flexible diaphragm 30- open to atmosphere on one sideand responsive on the other side to the pressure 10 minutes when the Iin the windbox i 5 and chamber l6 by reason of a conduit 3| whichconnects one side of the casing to the windbox. The switch 28 maybemounted upon the stoker hopper. A tension device 32 is carried by thecasing 29 to adjust the pressure necessary to cause the switchto-function under different conditions. A stem 33 moves with thediaphragm to open and close certain contacts as will appear later.

34 and 35 indicate respectively the main current conductors leading froma source of electrical energy or supply and secondary conductors 36-31connect one of the coils or windings of the transformer 23 with saidmain conductors. The main conductor 34 is connected to one side of thelimit control 22 and the other side of said control is connected to oneside of the coil of the relay 24 by a line 38 and in which is provided acontact 39. Cine side of the other coil or winding of the transformer 23is connected to one side of the coil of the relay 25 by a line 40 andthe other side of said other coil or winding of the transformer isconnected to one side of the thermostat 2| by a line 4|. The other sideof the thermostat is connected by a line 42 associated contacts 43 and39 respectively before mentioned. The armature 24a is connected incircuit to the main conductor 35 while the armature 25a is connected bya line 45 to the line 20 connecting one side of both motors l4 and 20together. A branch line 35a connects the other side of the blower motorl9 with the main conductor 35.

The time switch 25 includes a pair of fixed contacts 46-46a and a secondpair of contacts 4'|-4'|a, movable toward and away from the firstmentioned ones periodically. As shown herein, said switch includes amotor 48 that drives a shaft 48a, which carries cams 48b and 480. Thesecams so engage the contacts 41-41:; as to cause them to periodicallyengage and disengage said contacts 46-4611. The cam 48b is of suchformation that the contacts 46-4'| engage once about every ten minutesfor about a minute, but this time interval maybe changed by providingthe cam 48?) with a different number of faces. The cam 480 is of suchformation that the contacts Mia-41a engage once about every 60 minutesfor about one minute. The main conductor 35 leads to the contact whilethe contact 41 is connected by a line 49 to the other side of the 110Vcoil of the relay 24. The contact 41a is connected by a line 4|a to theline 4| and the contact 46a is connected by a line 42a to the line 42.Thus the contacts 4611-4111 are in the low voltage circuit and parallelwith the thermostat.

The pressure switch 28 includes a movable contact support 50 carrying acontact 5| which is connected in circuit to the line 49 by a line 53.

The support 50 is actuated by the stem 33 of the pressure switch formovement away from. and

"toward a fixed contact 52 which is connected in that the limit controlis functioning within itstemperature range as a closed switch. Also, as-

sume that the contacts 46-41 and 46a-41a of the timer switch 26 are outof engagement and that the thermostat 2| is in its off condition whereinit is not calling for heat. At this time both motors l4 and I9 aredeenergized and the pressure in the wind box l5 approximates atmosphericpressure so that the contacts 5|-52 of the pressure switch 28 areengaged.

Now assume that the temperature in the space to be heated is such thatthe thermostat 2| calls for heat and therefore closes. As the thermostatis closed, current flows through thesecondary of the transformer 23,line 4|, thermostat 2|, line 42, coil of relay 25,line 40, thuscompleting the circuit for the transformer.

This energizes the coil of the relay 25 to attract its armature 25awhich engages contact 39. control 22, contact 39, armature 25a, line '45to bridge 20, through the blower motor 19, line 35a to line 35, thusstarting the blower into operation. Also, if relay 24 has its armature24a engaged with the contact 43, current flows as before to bridge 20,through motor l4, line44 (and circuit breaker 21 therein which isclosed) to contact 43, armature 24a to line 35, thus energizing the fuelor coal feed motor l4.

The relay coil 24 will be held in its energized condition, with itsarmature 24a in engagement with the contact 43 so long as the contacts5|52 of the pressure switch 28 are engaged due to low pressureconditions in the wind box. With the contacts 5|-52 thus. engaged,current flows from the line 34, through the limit control 22, line 38,relay coil-24, line 49, contacts 5|'52, line 56, line 44, contact 43,armature 24a' to line 35. This holds the circuit for the relay coil 24closed.

With the stoker in operation, fuel is being fed to the burner or retortand air under pressure is being delivered to said burner or retort tosupport combustion. As the pressure builds up in the wind box, thecontacts 5|-52 separate,

opening the holding circuit for the relay coil 24 so that the armature24a disengages the contact 43. This opens the circuit for the fuel feedmotor |4 so that it stops the feeding of fuel. Later reengagernent ofthe contacts 5|--52 will not energize the relay coil 24 because there isno circuit to line 35 except when'relay coil 24 is energized.

Thus even though windbox pressure may drop to cause engagement of thecontacts 5|-52 the feed motor 4 willynot operate until the relay coil 24is energized by another circuit.

Closing of the circuit for the relay coil 24is accomplishedperiodically. by the constantly operating time switch 26. Every fewminutes the cam 48b of the time switch 26 will cause engagement of thecontacts 46-41 so that current will then flow'from line 34, through limt control 22, line 38, relay coil 24, line 49, contacts 414-46 to line35 so that the relay coil 24 be-- comes energized. This causes thearmature 24a to engage the contact 43,. permitting the switch 28 throughthe contacts 5|52 to mainta n current flow through the relay coil 24 andenergizing the coal feed motor M as before described. Thus, adiiferential in time is used for the starting of the fuel feed motor l4and a differential in pressure is used forstopping said motor.

This establishes a circuit from line 34, limit In the operation of thetime switch 26, it functions through the cam 480 to engage the contactsMia-41a which forms the "hold fire control of the system. As thesecontacts are in parallel with the thermostatfil, the engagement of thesaid contacts produces the same function as the closing of thethermostat '2| when it calls for heat. Should the limit control 22 be inits "ofP condition, current from the line 34 cannot pass to any of thebefore mentioned parts so that the stoker will not operateunder thatcondition.

It is important that the fuel feeding motor I4 should start whenever thethermostat 2| or the hold fire control (as caused by the engagement ofthe contacts 46a4|a) is calling for operation and this is accomplishedas follows: When the relay coil 25 is in its deenergized condition,current will flow from line 34, control 22, line 38, relay coil 24, line49, line 53, contacts 5| 52 (which because blower motor, I9 is notoperating will be in the engaged condition) through line 56, circuitbreaker 21, line 44, motor l4, bridge 20, motor l9, line 35a, line 35completing the circuit to energize the relay coil 24 and then hold it inclosed position until the thermostat 2| or hold fire control calls forstoker operation. .This circuit is possible because there is noresistance to the very .small amount of current passed by the relay coil24 due to the resistance of both motors l4 and I9 when not in operationand this small amount of current is notsuflicient the "hold fire controlcalls for operation of the stoker, this energizes the relay coil 25 asbefore described and causes the engagement of its armature 25a with thecontact 39. The motor I! then starts to drive the blower and to build upa' resistance in the last described circuit, after which the control ofthe fuel feed motor M will be effectedor come through the time switch 26and the pressure switch 28. It is apparent from the above, that the fuelfeed motor I4 is starte and stopped to control the fuel bed depth, steadof varying the feeding of fuel as in most conventional stokers. s

It is pointed out at this time that the amount of fuel which can beconsumed after the pressure switch 28 functions to separate the contacts5|-52 and previous to the time that the time switch 26 will startanother cycle of a feeding of coal to the fuel bed, will not besufllcient to change the depth of the fuel bed to any appreciableextent. However, it is desirable that the rate of fuel feed be higherthan the rate of combustion of :fuel. The reason therefor is in order toprovide against coking of the fuel in the retort and to vary the depthof the fuel somewhat at each operation so that the amount of fuel beingfed is sufficient to break up the fuel bed, each time fuel is being fed.The comparative short time whichis permitted between operations bytheswitch 26 after the closing of the pressure switch contacts 5|52 is notsufiicient to disturb the correct functioning of the stoker nor is theamount of coal fed by the operation of the switch 26 should the pressureswitch not be calling for fuel, sufficient to disrupt the operation tortadapted to support a fuel bed, means for' "pressure through said fuel'After a standby period, if the fuel bed isthin, the stoker is caused tofeed coal at its maximum rate until the fuel bed has been brought up toits proper depth after'which the fuel feed is operative only to anextent as will maintain that depth of fuel bed and to supply coal inaccordance with the amount thereof being burned with the volurns of airbeing supplied.

is is apparent from the above that through control of the fuel feed tomaintain a constant depth of fuel bed. a fixed resistance to passage ofair therethrough is obtained so that the windbox pressure is maintainedconstant and this constant resistance isobtained by the tendency of thewindbox pressure to vary in accordance with varying depth of fuel bedand this depth is maintained constant independent of the burning rate.

When the thermostat Ii is satisfied wlthheat, it opens-the circuit tothe relay coil so that the stcker stops.

While in describing the invention I have referred in detail to the form,arrangement and construction of the various parts" involved, the

same is to be considered only in the illustrative sense so that I do notwish to be limited thereto except as may be specifically set forth inthe appended claims. I claim as my inventions. 1. In combination withmeans providing arefeeding fuel to said retort to build up the bed to adesired depth, means for delivering air under pressure through said fuelbed to support combustion the I i, said bed oflering a resistance tosaid air so that its pressure varies with the depth or-density of thefuel bed, a circuit for said fuel feeding means andfor said airdelivering means respectively, means dependent upon the demandfor heatand operating 'through a part of said circuit for starting said airdelivering means, pressureresponsive means operative at one pressure ofthe delivered air for closing-another part of said'circuit for holdingsaid feeding means in operation and operating at another pressure of thedelivered air for stopping said feeding means, and means operatingautomatically through another part of said circuit at predeterminedtimed intervals for restarting said fuel feeding means independently ofsaid pressure responsive means when said means dependent upon demand forheat is holding said air delivering-means in opera.- tion. A

'2. In combination with means providing a retort. adapted to support afuel .bed, means for feeding fuel to said retort to build up the bed toa desired depth, means for delivering air under bed to supportcombustion thereof, said bed offering a resistance to saidair so thatits pressure varies with the depth or density of the fuel bed, a circuitfor said fuel. feeding means and said air delivering means respectively,means dependent upon the demand :for heat and operating through a partof said circuit for starting said air delivering means,pressureresponsive means operative at one pressure air for closinganother part of holding said -feeding means in said circuit foroperation and' operating at anotherpressure of thedelivered air forstopping said feeding means,

and means operating automatically through another part or saidcircuit-at predetermined timed intervals for restarting saidfuel-feeding means independently of said pressure responsive means whensaidmeans dependent upon demand for heat is holding said air deliveringmeans in operation, and means independent of said means dependent upondemand for heat for controlling said circuit for said fuel feeding meansand said air delivering means respectively. 7

, 3. In combination with means providing a retort adapted to support afuel bed, fuel feeding means and means for driving the same to build upthe fuel bed to a desired depth, means operable to provide air underpressure for delivery through said fuel bed to support combustionthereof, said bed offering a resistance to said air so that its pressurevaries with the depth or density of the fuel bed, means for driving saidair *delivery means, a circuit for bothof said driving means, meansdependent upon the demand for heat and operating through a part of'saidcircuit for starting said driving means for the 'air delivering means,pressure responsive ,means operating at one pressure of the deliveredair for closing another part of said circuitfor holding said drivingmeans for the fuel feeding means in operation,

and operating at another pressure of the delivered air for stopping saidfuel feed driving means, and means operating automatically throughanother part of said circuit at predetermined timed intervals forrestarting said fuel feed driving means independently of said pressureresponsive means when said means dependent upon the demand for heat isholding said air delivering means in operation.

4. In combination with means providing a retort adapted to support afuel bed, fuelfeeding means and means for driving the same to build upthe fuel bed to a desired depth, means operable to 'provide air underpressure for delivery through said fuel bed to support combustionthereof, said bed offering a resistance to said air so that its pressurevaries with the depth or density of the fuel bed, means for driving saidair delivery means, a circuit for both of said driving means, meansdependent upon the demand for heat and operating through a part of saidcircuit for starting said driving means for the air de1iv ering means,pressure responsive means operating at one pressure of the delivered airfor closing another part of said circuit for holding said driving meansfor the fuel feeding means in operation, and operating at anotherpressure of the delivered air for stopping said fuel feed driving means,and means operating automatically-through another part of said circuit,at predetermined timed intervals for restarting said fuel feed drivingmeans independently of said pressure responsive means when said meansdependent upon the demand for'heatis'holding said air delivering meansin operatiom-andmeans independent of said means dependent upon thedemand for heat,

for, controlling said circuit for said ,fuel feeding means and said airdelivering means respectively. 5. In combination with means providing aretort adapted to support a fuel bed, means for feeding fuel to saidretort to build up the bed to a desired depth, a motor for driving saidfuel feeding means, means operatively connected to the retort fordelivering air under pressure through the fuel bed to support combustionthereof, said bed offering a resistance to said air so that its pressurevaries with the depth or density of the fuel bed, a second motor fordriving the air delivery means, a circuit for both of said motors,meansdependent upon the demand for heat and operating through a part ofsaid circuit for starting said second motor, pressure responsive meansoperating at one pressure of the delivered air for closing another partof said circuit for holding said first mentioned motor in operation andoperating at another pressure of the delivered air for stopping saidfirst mentioned motor, and means operating automatically through anotherpart of said circuit, at predetermined timed intervals for restartingsaid first mentioned motor independently of said pressure responsivemeans when said means dependent upon the demand for heat is holding saidsecond mentioned motor in operation. a

6. In combination with means providing a, retort adapted to support afuel bed, means for feeding fuel to said retort to build up the bed to adesired depth, a motor for driving said fuel feeding means, a bloweroperatively connected to the retort for delivering air under pressurethrough the fuel bed to support combustion thereof, said bed offering aresistance to said air, so that its pressure varies with the. depth ordensity of the fuel bed, a second motor for driving said blower,

a circuit for both of said motors, means dependent upon the demand forheat and operating through a part of said circuit for starting theblower motor, pressure responsive means operating at one pressure of thedelivered air for closing a part of said circuit for holding the motorfor the fuel feeding means in operation and operative at anotherpressure of the delivered ai' r for stopping said motor for the fuelfeeding means, and means operating automatically through another part ofsaidcircuit at predetermined timed intervals for restarting the lastmentioned motor independently of said pressure responsive means whensaid means dependent upon the demand for heat is holding the blowermotor in operation,

' '1. In combination with means providing a retort adapted to support afuel bed, means for feeding fuel to said 1 retort to buildup the bed toa desired depth, means for delivering air under pressure through saidfuel bed to support combustion thereof, said bed offering a resistanceto said air so that its pressure varies with the depth or density of thefuel bed, a'circuit for said fuel a feeding means and said airdeliveringmeans respectively, means dependent upon the demand for heatand operating through a part of said circuit for starting said airdelivering means, pressure responsive means operativeat one pressure ofthe delivered air for closing another part of said circuit for holdingsaid feeding meansin.

operation and operating", at another pressure of r the delivered air forstopping said feeding means,

and means operating automatically through an other part of said circuit,at predetermined timed intervals for restarting said fuel feeding meansindependently of said pressure responsive means when said meansdependent upon demand for heat is holding said air delivering means inoperation, and means'for regulating the pressure.

- feeding means and said air delivering means respectively, meansdependent .upon the demand for heat and operating through a part of saidcircuit for starting said air deliveringmeans,

pressure responsive means operative at one pressure of the delivered airfor closing another part of said circuit for holding said feeding meansin operation and operating at another'pressure of the delivered air forstopping said feeding means, and means operating automatically throughanother part of said circuit, at predefeeding means independently of,said pressure responsive means when said means dependent upon demand forheat is holding said air delivering means in operation, means forregulating the pressure of air delivered to said retort to control theburning rate of the fuel bed, and means for adjusting the operativepressure of said pressure responsive means.

9. In combination with means providing a retort adapted to support afuel bed, fuel feeding means and a motor for driving the same to buildup the fuel bed to the desired depth, a circuit for said motor, meansfor delivering air under pressure to said fuel bed to support combustionthereof, said bed ofiering a resistance to said air so that its pressurevaries with the depth or density of the fuel-bed, means dependent uponthe demand for heat for starting the air delivering means intooperation, pressure responsive means operating at one pressure of thedelivered air for holding the motor circuit closed and operating atanother pressure of the de- .livered air for opening said motor circuit,and

' termined timed intervals for restarting said fuel I circuit for saidmotor, means for delivering air under pressure to said fuel bed tosupport combustion thereof, said bed ofiering a. resistance to said airso that its pressure varies with the depth or density of the fuel ,bed,means dependent upon the demand for heat for starting the air deliveringmeans into operation, pressure responsive means operating at onepressure of the delivered air for holding the motor circuit closed'andoperating at another pres-- sure of the delivered air for opening saidmotor circuit, meansoperating automatically at predetermined timedintervals for closing said motor circuit independently of ,said pressureresponsive means when said means dependent upon the demand for heat isholding said air deliverin'g means in operation, and means forregulating the pressure of the air delivered to said retort to controlthe burning rate of the fuel bed.

11. In. combination with a stoker'including a: retort adapted tosupporta bed of fuel thereon,

a means for feeding fuel to the retort to build up the bed to thedesired depth, a motor for driving said means, a blower and a motor fordriving the same and a windbox connecting said blower and the retort todeliver air under pressure to s id retort for passing through the'fuelbed, said; (1

offering a resistance to the passage of air therethrough so that saidpressure varies with the starting said motor, means responsive towindbox pressure and operating at one pressure of the air therein forclosing that part of said circuit to hold the fuel feed driving motor inoperation, and operating at another" pressure of the air in the windboxfor stopping said motor, and means operating automatically through saidcircuit at predetermined timed intervals for restarting the fuel feed.driving motor independently of said pressure responsive means, when saidblower motor circuit is being held closed by said means responsive tothe demand for heat. a

12. In combination with a stoher including a retort adapted to support abed of fuel thereon, means forfeeding fuel to the retort to build upsaid bed to the desired depth, a motor for driving said means, a blowerand a motor for driving the same and a windbox connecting the blower andthe retort to supply air under pressure to said retort for passingthrough the fuel bed to support combustion thereof, said bed offering aresistance to the passage of air therethrough so that the pressure inthe windbox varies with the depth or density of the fuel bed, a circuitfor both of said motors, means dependent upon the demand for heat forclosing that part of said circuit which will start said blower motor,means responsive to the pressure in the windbox and operative at onepressure. therein for closing that part of said circuit that will holdthe fuel feeding means driving motor in operation and operative atanotherpressure in the windbox for opening-said part of the circuit tostop said fuel feeding means driving motor, and a constantly runningtime switch for closing said last mentioned part of said circuit atrelatively short intervals to restart said fuel feeding means drivingmotor independently of said pressure responsive means when said firstmentioned part of the circuit is being held closed by.said meansdependent upon the demand for 13. In combination with a stoker includinga retort adapted to support .a bed of fuel thereon,

means forfeedingfuel to the retort to build up said bed to the desireddepth, a mot'orfor'driving bed, a circuit far said motors, meansdependent upon the demand for heat for closing that part of said circuitwhich will start said blower motor, means responsive to the pressure inthe windbox and operativeat one pressure therein for closing that partof said circuit that will hold the fuel feeding means dri'vingmotor inoperation and operative at another pressure in the windbox for openingsaid-part of the circuit to stop said fuel feeding means driving motor,a'constantly running time switch for closing said :mentioned part ofsaid circuit at relatively ort intervals to restart said fuelfeedingmeans driving motor independentlyeof said pressure responsive means whensaid first mentioned part of the circuit is being held closed by saidmeans dependent upon the demand for heat, and means formulating .thepressure of the air delivered by the blower to the retort-"to controlthe burning rate of the, fuel 14; In combination with a stoker includinga retort adapted to support a bed of fuel thereon. means forfeeding fuelto the retort to build up said bed to the desired depth,a motor fordriving said means, a blower and a motor for driving the same and awindbox connecting the blower and the retort to supply air underpressure to said retort for passing through the fuel bed, said bedoffering a resistance to the passage of air therethrough so that thepressure in the windbox varies with the depth or density of the ,fuelbed, a. circuit for said motors, a relay in that part of said circuitassociated with the blower motor and controlling said part of saidcircuit, a second.relay in another part of said circuit associated withthe fuel feeding means driving motor, means dependent upon the demandfor heat and causing said first mentioned relay to close its associatedpart of the circuit to start the blower motor, means responsive towindbox pressure and operative at one pressure to energize said secondrelay to close that part of the circuit associated withthe fuel feedingmeans driving motor'whereby said motor is held inofieration, saidpressure responsive means operating at another pressure in the windboxfor deenergizing said second relay to stop the last mentioned motor, anda constantly running time switch operating at intervals for energizingsaid second relay independently of said pressure responsive means torestart said fuel feeding means driving motor when said first mentionedrelay is being held closed by said means responsive to the demand forheat. 15. In combination with a Stoker inclu g a retort adapted tosupport a bed of fuel thereon, means for feeding fuel to the retort tobuild up said bed to the desired depth, a motor for driving said means,a blower and a motor for driving the same and a wlndbox connecting theblower and the retort to supply air under pressure to said retort'forpassing through the fuel bed, said bed offering a resistance to thepassage of air there-- through so that the pressure in the windboxvaries with the depth or density of 'thefuel bed, a circuit forsaidmotors, a relay, in that part of sai circuit associated with theblower motor and cohtrollingsaid part of said circuit,-a second relay inanother part of said circuit associated with the fuel feeding meansdriving motor, means dependent upon the demand for'heat and causing saidfirst mentioned relay to close its associated part of the circuit tostart the blower motor, means responsive to windbox pressure andoperative at .one pressure to energize said second relay to ciose thatpart of the circuit associated with the fuel is held in operation, saidpressure responsive means operating at another pressure in the windboxfor deenergizing said second "relay to stop feeding means driving motorwhereby said motor the last mentioned motor, and a constantly runningtime switch operating at intervals for energizing said second relayindependently of said gpressure responsive means to restart said fuelfeeding means driving motor when said first mentioned relay is heldclosed by said' means responsive to the demand for-heat. said circuitbeing arranged to close the-relay for the driving motor forthe fuelfeeding means when said blower motor is inoperative so that said fuelfeeding meansdriving motor will become energized by saidmeansdependentupon the demand-for heat when the latter operates to cause itsrelay to close its associated part of the circuits a ROBERT E. BRESSIER.

